Polyurethane foam systems, for example, usually include component A, an isocyanate, and component B, a preformulated compound comprising a polyether resin, a catalyst, a surfactant and a blowing agent. Each component of the plural material is, by itself, generally stable, that is, each component does not cure or cross-link for several months or more, provided it is properly stored. However, mixing of component A and component B in proper concentrations initiates a chemical reaction that causes the components to begin to polymerize and generate heat which volatilizes the blowing agent and causes the polyurethane to foam, cure and cross-link. In one polyurethane system, water is used to combine with isocyanate to provide a carbon dioxide blowing agent; and in another polyurethane system, a fluorocarbon or Freon, which boils at about room temperature, provides the blowing agent. In this system, the blowing agent is trapped in the resin and acts in cooperation with the other constituents of the system to foam the polyurethane. Other systems may be such that the blowing agent is used to provide a cellular structure.
Usually cross-linking and curing of a plural component material is substantially completed in a matter of seconds. It is therefore desirable to mix the components in the dispensing device as close as is possible to the orifice from which the mix is ejected, that is, mixing of the several components of the compound should take place substantially contemporaneously with dispensing. Mixing the components of the plural component material with the dispensing device requires the apparatus operator to purge the residue of the mixed components from a mixing chamber and the orifice of the dispensing device so that the residue components do not chemically react and clog the chamber and the orifice, or in any other way prevent or inhibit dispensing of the plural component material.
U.S. Pat. No. 3,799,403, issued to Richard O. Probst et al. discloses an apparatus for mixing and dispensing plural component materials, such as urethane foam materials. The Probst et al. patent discloses a hand gun which includes a mixing and dispensing element that is movable with respect to the housing of the device between a rearward position, at which the components of the plural component material are introduced into a mixing chamber in the mixing and dispensing element, appropriately mixed and then dispensed, and a forward position, at which the introduction of components into the mixing chamber is terminated, and air is introduced into the mixing chamber to substantially purge residue material from the mixing chamber and its cooperatively associated orifice.
In the gun disclosed by the Probst et al. patent, the movable mixing and dispensing element forms, in combination with a pair of connection blocks carried by the gun housing, the valves that control the mixing and dispensing of the plural component material. The connection blocks are connectible with the separate pressurized sources of the components of the plural component material and include outlet openings and carry plastic seal members around the outlet openings that interface with and seal against the sides of the mixing and dispensing orifice. The movable mixing and dispensing element includes an internal mixing chamber between its sides, a pair of admission openings, one between each side of the mixing and dispensing element and its internal mixing chamber, and a forward-most dispensing orifice connected with the mixing chamber. When the mixing and dispensing orifice is in its rearward position, the admission openings on each of its sides are aligned with the outlet openings of the connection blocks so the components of the plural component material can flow from their separate pressurized sources into the mixing chamber, where they are mixed and urged out of the dispensing orifice. When the mixing and dispensing element is in its forward position, the outlet openings of the connection blocks are blocked by the sides of the mixing and dispensing element, terminating the dispensation of mixed plural component materials. In the rearward position, the seals carried by the connection blocks confine the flows of the plural components to between the connection block-outlet openings and the admission openings of the mixing and dispensing element, and in the forward position, the seals prevent the plural components from flowing into the interface between the mixing and dispensing element and the connection blocks.
The housing of the device disclosed by the Probst et al. patent includes an air-operated piston/cylinder that is connected to the mixing and dispensing element to move it between its forward and rearward positions. A trigger on the handle of the hand gun controls the application of compressed air, through a four-way valve, to the portions of the cylinder on each side of a piston to move it forwardly and rearwardly within the cylinder, thus moving the mixing and dispensing element between its rearward mixing and dispensing position and its forward position at which the flow of plural component material is terminated and the mixing chamber is purged.
Plural component guns like those disclosed in the Probst et al. patent have been sold for almost 30 years by Glas-Craft, Inc., with the registered trademark PROBLER®.
More recently, such guns have incorporated an improved air actuator for controlling the flow of plural component material from the gun, as disclosed in U.S. Pat. No. 6,796,461 issued to Steven Sinders. In the improved air actuator, two serially connected pistons operating along a common axis within two separate cylinder portions of the housing drive the mixing and dispensing element back and forth along the common axis by the application of compressed air to the two separate cylinder portions of the housing.
Nevertheless, in such guns, it has been difficult to obtain consistently effective mixing of the plural component materials and wide and uniform spray patterns of the mixed plural component materials with the mixing and dispensing element of the apparatus.